FIG. 1 is a circuit diagram illustrating a structure example of a temperature sensor circuit. The temperature sensor circuit generates a current I proportional to temperature by using a potential difference generated between collectors of two npn bipolar transistors 101 and 102 different in emitter size. However, in a CMOS process that does not allow the use of a triple well process, the npn bipolar transistors 101 and 102 cannot be used. Therefore, when the CMOS process is used, the temperature sensor circuit in FIG. 1 cannot be manufactured. Further, when the triple well process is used, it is necessary to separate wells, which has a problem of an increase of the area of the temperature sensor circuit.
FIG. 2 is a circuit diagram illustrating a structure example of another temperature sensor circuit. The temperature sensor circuit has MOS field-effect transistors 203 to 205 and pnp bipolar transistors 201, 202 and generates a current I proportional to temperature by using a potential difference generated between emitters of the two pnp bipolar transistors 201 and 202. Even when the CMOS process is used, the pnp bipolar transistors 201 and 202 can be used. However, using the pnp bipolar transistors 201 and 202 leads to a problem of an increase of the area.
Further, a temperature detecting device having a first MOS transistor and a second MOS transistor has been known (refer to Patent Document 1). A potential control circuit detects a potential under a gate of the first MOS transistor at the depletion time, and controls a gate voltage of the first MOS transistor based on the detected potential. A gate voltage of the second MOS transistor is controlled by the potential control circuit and an output of the second MOS transistor is a temperature output.
Patent Document 1: Japanese Laid-open Patent Publication No. 09-133587
Since the temperature sensor circuit in FIG. 1 uses the npn bipolar transistors 101 and 102, it is necessary to separate the wells when the CMOS process is used, which has a problem of the increase of the area. Further, the temperature sensor circuit in FIG. 2 has a problem of the increase of its area because of the use of the pnp bipolar transistors 201 and 202.